1. Field of the Invention
The present invention relates to a light modulation device used for optical information processing, and to an image recognition method for processing images using a neural network constructed to simulate the information processing mechanism of the human brain.
2. Prior Art
Information processing devices based on neural networks have been studied in recent years, and the optical neural network in particular has been developed as an effective means of high speed processing of two-dimensional image data (M. Ishikawa, et al., Applied Optics, Vol. 29, No. 2, pp. 289-295 (1990)). The optical neural network uses an optical signal as the data medium due to its high speed transmission capability and spatial parallelism properties. The spatial light modulation device is a key component to the construction of an optical neural network.
FIG. 24 is a cross section of a conventional spatial light modulation device 1 comprising a transparent electrode 2, a photoconductive layer 3, a light reflecting layer 4, a light modulation layer 5, and a second transparent electrode 2' formed together in that order and sandwiched between a substrate 6 and 6' on each side. This device operates as follows.
When an input light 7 with a two-dimensional distribution of light intensity is incident on the photoconductive layer 3, carriers corresponding to the light distribution are produced and the electrical resistance of the area of the photoconductive layer in which the light is incident on 3 drops. A voltage is applied between the transparent electrodes 2 and 2', and the voltage applied to the light modulation layer 5 increases at the area corresponding to the area in which the electrical resistance dropped in the photoconductive layer 3. Thus a read light 8 is spatially modulated according to the light distribution of the input light 7. The light reflecting layer 4 is simply provided to efficiently reflect the read light 8.
3. Problem to be Solved
Accurately and quickly extracting features peculiar to the image is essential to improving the recognition performance of an optical neural network.
However, the conventional spatial light modulation device simply functions as an image input device and does nothing more than execute simple logic operations such as digitization resulting from the light modulation characteristics of the light modulation layer. It is impossible for these devices to extract the specific features of the image.
Furthermore, extracting the specific features of the input image requires the input image to be photoelectrically converted and stored in an image memory for feature extraction processing by an electronic computer. This process is time-consuming and processing time will increase when the matrix of the image is increased.